Typical solid state memory devices (dynamic random access memory (DRAM), static random access memory (SRAM), erasable programmable read only memory (EPROM), and electrically erasable programmable read only memory (EEPROM)) employ micro-electronic circuit elements for each memory bit in memory applications. Since one or more electronic circuit elements are required for each memory bit, these devices consume considerable chip space to store information, limiting chip density. For typical non-volatile memory elements (like EEPROM i.e. “flash” memory), floating gate field effect transistors are employed as the data storage device. These devices hold a charge on the gate of the field effect transistor to store each memory bit and have limited re-programmability. They are also slow to program.
PRAM (Phase Change Access Memory) devices (also known as Ovonic memory devices) use phase change materials (PCMs) that can be electrically switched between an insulating amorphous and conductive crystalline state for electronic memory application. Typical materials suited for these applications utilize various chalcogenide (Group VIB) and Group VB elements of the periodic table (e.g., Te, Po, and Sb) in combination with one or more of In, Ge, Ga, Sn, or Ag (sometimes referred to herein as a “phase change alloy”). Particularly useful phase change alloys are germanium (Ge)-antimony (Sb)-tellurium (Te) alloys (GST alloys), such as an alloy having the formula Ge2Sb2Te5. These materials can reversibly change physical states depending on heating/cooling rates, temperatures, and times. Other useful alloys include indium antimonite (InSb). The memory information in PRAM is preserved with minimal loss through the conductive properties of the different physical states.
Compositions and methods for chemical-mechanical polishing (CMP) the surface of a substrate are well known in the art. Polishing compositions (also known as polishing slurries, CMP slurries, and CMP compositions) for CMP of metal-containing surfaces of semiconductor substrates (e.g., integrated circuits) typically contain an oxidizing agent, various additive compounds, abrasives, and the like.
In conventional CMP techniques, a substrate carrier or polishing head is mounted on a carrier assembly and positioned in contact with a polishing pad in a CMP apparatus. The carrier assembly provides a controllable pressure to the substrate, urging the substrate against the polishing pad. The pad and carrier, with its attached substrate, are moved relative to one another. The relative movement of the pad and substrate serves to abrade the surface of the substrate to remove a portion of the material from the substrate surface, thereby polishing the substrate. The polishing of the substrate surface typically is further aided by the chemical activity of the polishing composition (e.g., by oxidizing agents present in the CMP composition) and/or the mechanical activity of an abrasive suspended in the polishing composition. Typical abrasive materials include silicon dioxide, cerium oxide, aluminum oxide, zirconium oxide, and tin oxide.
U.S. Pat. No. 5,527,423 to Neville, et al., for example, describes a method for chemically-mechanically polishing a metal layer by contacting the surface of the metal layer with a polishing slurry comprising high purity fine metal oxide particles suspended in an aqueous medium. Alternatively, the abrasive material may be incorporated into the polishing pad. U.S. Pat. No. 5,489,233 to Cook et al. discloses the use of polishing pads having a surface texture or pattern, and U.S. Pat. No. 5,958,794 to Bruxvoort et al. discloses a fixed abrasive polishing pad.
CMP techniques can be utilized to manufacture memory devices employing phase change materials; however, current CMP compositions do not provide sufficient for planarity when utilized for polishing substrates including relatively soft phase change alloys, such as a GST or InSb alloy. In particular, the physical properties of many phase change alloys (e.g., GST or InSb) alloys make them “soft” relative to other materials utilized in PCM chips. For example, typical CMP polishing slurries containing relatively high solid concentrations (> about 3%) remove a phase change alloy (e.g., a GST alloy) through the mechanical action of the abrasive particles resulting in heavy scratching on the surface of the phase change alloy. When such high solids CMP compositions are used, phase change alloy residues often remain on the underlying dielectric film after polishing, since the CMP slurry is not able to remove all of the phase change alloy material. The phase change alloy residues cause further integration issues in subsequent steps of device manufacturing.
There is an ongoing need to develop new CMP compositions that exhibit reduced scratching and residue defects, while still providing acceptably rapid removal of phase change alloys compared to conventional CMP compositions. The present invention provides such improved CMP compositions. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein